Been racking my brain and wearing out my google button on the subject of a bulk thermal insulation to use in van walls, side doors, etc.
Fiberglass: cheap limp, sags, breaks down into particulates absorbs moisture
Thinsulate: expensive limp, sags, doesn't break down doesn't absorb moisture
Rockwool: not cheap not limp, doesn't sag, doesn't break down doesn't absorb moisture
Clarifications: Cheap means cheapest practical thing, expensive means most expensive thing I'd consider, not cheap is somewhere in the middle.
Limp, sags, etc means it needs to be attached and supported so it doesn't fall and create gaps or get compacted, which would lower its effectiveness. Breaking down isn't really a concern of mine, as I plan to seal the walls. Read on for an idea that spurred this thread.
Absorbing moisture means it either does or does not hold moisture, lowering its efficiency and causing rust. This moisture comes primarily from respiration and from a warm van in cold weather and a cold van in warm weather.
So here's my idea: use the cheap limp stuff, but structure it in "bags" of Tyvek, a one-way breathable vapor barrier.
The problem I'm trying to solve is that the walls of the van are closed off from it's exterior by steel, which I plan to paint with DIY lizardskin, http://67-72chevytrucks.com/vboard/show ... p?t=511370
, then add a sound barrier/isolator/absorber (whatever you want to call it, I'm not being overly technical here) like FatMat, Dynamat, or that cheap roofing ice barrier from Lowe's/Home Depot. To seal this in with Reflectix or some such vapor barrier (an absolute barrier, think ziplock baggy) means there absolutely will
be condensation that you hope runs down the wall and out the OE (or additional) drain holes. The vapor barrier does prevent your breath from reaching the exterior walls but it doesn't prevent environmental condensation and I assume anybody converting/insulating a van will condition (heat or cool) its interior. With solid steel on the outside and a solid vapor barrier on the inside, there is no air movement within the walls to dry this condensation, so gravity/the motion of the van are your only hopes of it migrating out. My idea is that a one-way vapor barrier can keep your breath from reaching the walls but can also allow air movement into the wall cavities, thus helping to dry them. So what I'm proposing is a bag, or envelope really, of tyvek that matches a cavities dimensions, plus maybe 2" in each dimension, filled with bulk, un-faced insualtion. The 2" flange around the edges will allow them to be attached to the walls themselves, on the interior side, and prevent the insulation from sagging and also contain their particulates. I think it would be best to adhere the insulation to at least one side of the bag so it doesn't sag within it but I also think slightly
compressing the insulation, which might require it be built up in multiple layers in some areas, would help it stay in place, much the same as gluing it in place without stuffing
it into cavities as we've all seen done.
Thoughts? Suggestions? Positive or Negative are welcome, I'm here to learn not be patted on the back.